fyi inside building must have signal booster and it is the building owner's responsibility to install it.

Yes definitely sucks indoor. dont even say indoor, even at outdoor tepi jalan mamak also i cant get a working stable signal under zinc roof.
to port out u need to inform and apply at Yes and reply sms. u need to make sure line is active (not in grace period).
once port out approved, u need to get a hotlink simcard or unless u opt for e-sim, u can straight register in hotlink app.

Try to enter your Yes mobile number. From the instruction it is stated: "If you are a Non-Maxis user please enter your mobile number."
If still cannot then find a deeler or visit Maxis centre to do the MNP.
Please be firm, tell them you only want to port in to Hotlink prepaid. They might try to sell postpaid plan to you.